igneous
Tumbled dark stone, likely basalt or basaltic rock
Fine-grained mafic igneous rock; commonly basalt, composed mainly of plagioclase and pyroxene with possible olivine
AI-generated identification · may be incorrectDark gray to black, rounded and polished with a dull-to-submetallic luster; typically massive and fine-grained, Mohs hardness about 5–6, with no visible cleavage. The photograph is insufficient for a definitive identification.
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Physical properties
Dark gray to black, rounded and polished with a dull-to-submetallic luster; typically massive and fine-grained, Mohs hardness about 5–6, with no visible cleavage. The photograph is insufficient for a definitive identification.
Formation & geological history
Basalt forms when mafic lava cools rapidly at or near Earth’s surface, commonly during Cenozoic to modern volcanic activity; its minerals crystallize microscopically. This specimen appears human-tumbled or polished.
Uses & applications
Used as aggregate, roadstone, building stone, and landscape material; small polished pieces are sold as inexpensive curios or worry stones. Typical value is low.
Geological facts
Basalt is the most abundant volcanic rock on oceanic crust and commonly forms lava flows, dikes, and pillow lavas.
Field identification & locations
Look for a uniformly fine texture, high density, dark color, and lack of visible quartz or large crystals; a streak, magnetism test, and fresh fracture can help distinguish it from slag, hematite, or other dark stones. Common worldwide, especially volcanic regions.
